Our U.S. Pat. No. 4,374,248, issued Feb. 15, 1983, discloses 3,4-disubstituted-1,2,5-thiadiazole 1-oxides and 1,1-dioxides having the formula ##STR5## and processes for their preparation, wherein the variables A, m, Z, n and R.sup.1 are similar to the corresponding substituents of the compounds disclosed and claimed herein. However, the compounds disclosed therein are 1-oxides or 1,1-dioxides (p is 1 or 2), and the compounds of the present invention cannot be prepared by any of the processes described therein for the preparation of the prior art compounds.
European Patent Application No. 40,696 published Dec. 2, 1981 discloses inter alia 3,4-disubstituted-1,2,5-thiadiazole-1-oxides and 1,1-dioxides having the formula ##STR6## and processes for their preparation, wherein the variables R, .circle.A , n, X, m, R.sup.1 and R.sup.2 are similar to the corresponding substituents of the compounds disclosed and claimed herein. However, the compounds disclosed therein also are 1-oxides or 1,1-dioxides (p is 1 or 2) and the compounds of the present invention cannot be prepared by any of the processes described therein for the preparation of the prior art compounds.
In the two publications cited above, each of the processes described for preparation of the prior art compounds involves the use (as a starting material or intermediate) of a 1,2,5-thiadiazole 1-oxide or 1,1-dioxide having either amino groups or suitable "leaving groups" on the 3- and 4-positions. The desired substituents on the 3- and 4-positions are then obtained by substitution on the amino groups or by replacement of the "leaving groups". We have made extensive attempts to prepare the compounds of the present invention by similar procedures, i.e. by utilizing 1,2,5-thiadiazole having amino groups or suitable "leaving groups" on the 3- and 4-positions as starting materials or intermediates. Although numerous variations were tried, along with varying reaction conditions, we were not able to isolate the compounds of this invention by that route.
We have now found that the compounds of the present invention may be prepared by ring closure of the correspondingly substituted ethanediimidamide of the formula ##STR7## Intermediate II, itself, may be prepared by various procedures.